Born in Inishowen, Co. Donegal (Ireland), John Toland (1670-1722) was one of the most significant Anglophone intellectuals of the early 18th century. He blazed a remarkable trail across Europe, becoming famous - and infamous - as philosopher, scholar, freethinker, pamphleteer, controversialist, and scourge of political and religious conservatives. He became directly acquainted with so many of the great philosophical and political figures of his age, working tirelessly on all fronts to further the cause of the early Enlightenment. And, as part of this labor, he produced philosophical texts which are only now being appreciated for their insight, perspicuity, and creative profundity. John Toland's Letters to Serena is one of the most important texts of the early Enlightenment. Synthesizing an array of European thought - from radical biblical hermeneutics to republican politics; from ancient Stoicism to Newtonian physics; from 'sociology' avant la lettre to the metaphysical speculation of Leibniz and Spinoza - Letters to Serena was not only significant for Toland's own 'freethinking' cause, but also provided crucial foundations for the 'vitalist' materialism characterizing later Enlightenment thought. Despite the historical and intrinsic significance of the text, this is the first modern, English-language edition of the Letters since its original publication in 1704. Accordingly, the editor of this study provides a comprehensive introduction, a contextual 'timeline, ' full annotations, and a bibliography. As the introduction suggests, this long overdue edition of a book that bursts with ideas, intellectual energy, and brilliant crackling prose will allow something of John Toland's full force to be felt again, more than three centuries after its original, explosive, manifestation